As is known, a power supply device for a household appliance, such as a cook-top or a microwave oven, generally comprises an AC-AC switching converter, which provides a driving current having adjustable frequency and amplitude to feed a load, such as the induction coil of a cook-top or the primary winding of a step up transformer feeding a magnetron device.
Quasi-Resonant (Q-R) converters are widely used in power supply devices for household appliances, since they can adjust the switching frequency or duty-cycle to ensure that the switching converter is constantly switching in zero voltage/current conditions (“soft switching” operation) and are generally characterised by a relatively simple circuit structure.
In a power supply device for a household appliance, a controller is typically adopted for controlling the operation of the switching converter.
Such a controller operates in a continuous regime and performs a cycle-by-cycle regulation of the input current (or power) adsorbed by the power supply device.
Often, PWM modulation techniques are adopted to adjust a control quantity used for controlling the switching converter (e.g. the switching frequency or duty cycle), so that the input current follows a reference value (set-point).
Regardless of the kind of control loop that is adopted, a feedback signal, indicative of the input current that is actually adsorbed from the main power input by the power supply device, is generally required in order to calculate the current (or power) error between the current (or power) reference and the current (or power) that is actually adsorbed.
Traditionally, such a feedback signal is obtained by properly arranging a current sensor, e.g. a current transformer, a Hall Effect sensor, a shunt circuit or the like that is embedded within the power supply device.
The adoption of a dedicated current sensor entails an increase of the overall size of the power supply device and the need of arranging a relatively complex circuit structure.
Of course, these drawbacks determine an increase of the costs for manufacturing the power supply device at industrial level.